I. Field of the Invention
This invention relates generally to hand trucks for moving heavy loads, and more particularly, to an electric motor powered hand truck for raising and lowering heavy loads, that hand truck being designed to be highly maneuverable when either loaded or unloaded by a single operator.
II. Discussion of the Prior Art
The closest prior art which I am aware is my own earlier electric hand truck described in U.S. Pat. No. 4,034,878, the teachings of which are hereby incorporated by reference. The present invention is considered to be a marked improvement over the product corresponding to my ""878 patent. Specific features considered to be improvements include, but are not limited to:
1. My new hand truck provides for both negative and positive lifting of a load. That is to say, with the floor as a reference, the hand truck of the present invention is capable of not only lowering a load below floor level, for example, at a loading dock, but is also capable of elevating the load above the floor as with a fork lift. It also has the ability to climb stairs and get into a truck with a full load on it.
2. My new design is of lighter weight construction, without a sacrifice in strength or load carrying capability. This is achieved by utilizing inner and outer side rails comprising aluminum extrusions for the vertical frame members, where the extrusions are designed to interlock, yet slide relative to one another without binding.
3. Improved mobility of the unit is assured by providing a plurality of swivel casters on the underside of the main load plate which attaches to the inner side rail extrusions of the vertical frame members and with the hand cart""s main wheels journaled for rotation on a main frame casting that is affixed to the outer side rails of the left and right interlocking extrusions forming the vertical frame members.
4. Load bearing forks are pivotally mounted on the main frame casting and when lowered parallel to the ground, they straddle the load plate. The pivotal load arms are deployed when taking advantage of the positive lift feature of the hand cart, but are swung up and out of the way when utilizing the negative drop feature.
5. A motor driven lead screw is operatively coupled between the main frame casting and a top member spanning and affixed to the outer side rail extrusions and the lead screw cooperates with a traveling nut mounted on a top plate spanning the inner side rail extrusions. Thus, as the electric motor drives the lead screw, the inner and outer side rail extrusions are longitudinally displaced relative to one another in a direction depending upon the direction of rotation of the motor.
6. The interlocking side rail extrusions include longitudinal grooves extending the length thereof for permitting the attachment of a stabilizing carriage frame that is supported in a cantilevered dolly fashion toward the rear of the hand truck and which also has swivel caster wheels affixed to the underside thereof for engaging the ground when the hand truck is tilted back at an angle to the vertical. The slots in the side rail extrusions also permit flexible cinch belts to be used to secure a load onto the handcart.
7. The use of elongated lineal contact electrical switch strips mounted on the outer one of each of the extruded side rails makes it easy for an operator to control energization of the motor from a point anywhere along the side rails, thus obviating the need to search for a small on/off switch as in the prior art.